Download P31.14 Herbs are hurt, shrubs will thrive in a warmer arctic climate

Climate Change: Global Risks, Challenges and Decisions
IOP Conf. Series: Earth and Environmental Science 6 (2009) 312022
IOP Publishing
doi:10.1088/1755-1307/6/1/312022
P31.14
Herbs are hurt, shrubs will thrive in a warmer arctic climate: Results of ITEX - The International
Tundra Experiment
Per Mølgaard
University of Copenhagen, Department of Medicinal Chemistry, Copenhagen, Denmark
It was said that a global climate change would first and most severely take place in Arctic, terrestric
ecosystems. A rapid change in plant performance took place in a fell field area near the Arctic Station on
Disko in 1996, coinciding with a marked decline in winter ice coverage in the Disko Bay in West Greenland.
Most climate models have shown that global warming will take place earlier and that the effects will be
more severe in the Arctic than elsewhere. This was the background for establishment in 1990 of ITEX – the
International Tundra Experiment – as a collaborative, circumpolar experiment using a common design to
examine variability in species response to temperature manipulation. At all sites, the same sets of
observations were carried out according to a protocol outlined in the ITEX Manual (Molau and Mølgaard
1996). The common design agreed upon for temperature enhancement was sets of open top chambers that
would lead to a temperature increase averaging 2 - 3 oC, which was the expected range after 50-100 years
according to Intergovernmental Panel on Climate Change (IPCC 2001). The participants were researchers
with activities located at stations in the Arctic, e.g. North America, Europe and Russia; in Greenland with
the present author as Danish representative. The purpose of ITEX was on a general level to find measures
for plant responses to experimental warming, anticipating the effect on individual species of the expected
global warming. Alongside the experimental warming, the gradual development in plant performance was
monitored, with emphasis on registration of annual growth, flowering, and seed set for selected,
characteristic and common Arctic plant species. A long term change in plant performance was expected if
the sequence could be carried out for en extended period of time. More immediate results would be obtained
from the manipulation experiment. The first results of this multisite temperature manipulation were
published as Supplement 1 to volume 3 of Global Change Biology in 1996, e.g. (Henry and Molau 1997,
Marion et al. 1997, Mølgaard and Christensen 1997). The first common paper was published by Ecological
Monographs (Arft et al. 1999) and known as ‘the multi-author paper of ITEX’. In these publications we only
gave results from 3-4 years of experimental warming, however, the results showed a marked effect of the
experimental warming from all 13 sites involved in the experiment. The latest common paper (Walker et al.
2006) gives the results on the community level. This conference contribution will be a presentation of the
general results from the common ITEX program seen in perspective of the subsequent change in climate
conditions which turned out to be sooner and more severe than first anticipated. The common result of the
experimental warming around the plants was a significant increase in vegetative growth, in biomass and in
seed set at all 13 sites involved in the experiment. A monitoring programme was established at Zackenberg
in Eastern North Greenland inspired by the ITEX activities and showed after the first ten years, that the
duration of the snow cover and hence the onset and length of growth period was a more determining
parameter for plant growth than mean summer temperature (Mølgaard et al. 2002). In more detail, the results
from the Greenland sites will be shown. After the first three years with experimental warming around
rosettes of the arctic poppy (Papaver radicatum) there was a decline in the above ground biomass. At that
time, temperature was no longer limiting plant performance, but the available plant nutrients were exhausted
due to exaggerated growth (Mølgaard and Christensen 1997). We now have an 18 year long regular series of
observations of P. radicatum with respect to fluctuations in population structure and individual plant
biomass. During the first years, there was a slight increase in the poppy biomass and in number of plants,
indicating a rather stable community and population structure. In 1996, this period was followed by a
dramatic decrease in number of plants and recruitment of seedlings together with a loss of above ground
plant biomass, especially in wind swept fell field areas with low snow cover (Fig.1). This change in plant
performance coincided with a sudden change in winter ice coverage in the Disko Bay (Fig.3) (Hansen et al.
2006, Nielsen et al. 2000), and several thaw periods during the winter with bare frost, intolerable to the
poppy plants. At the same time a gradual increase took place in the ground coverage of Arctic willow (Salix
arctica) (Fig.2), a trend very much comparable to the onset of a general secondary succession, where
willows seem better to tolerate the exposure to milder, but more unstable winter conditions.
c 2009 IOP Publishing Ltd
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Climate Change: Global Risks, Challenges and Decisions
IOP Conf. Series: Earth and Environmental Science 6 (2009) 312022
IOP Publishing
doi:10.1088/1755-1307/6/1/312022
Development of
Papaver radicatum
Biomass estimate
20000
LOC. 4
15000
LOC. 7
10000
5000
0
19
89
19
91
19
93
19
95
19
99
20
03
Fig.1. Development in estimated plant biomass for two populations of Arctic poppy (Papaver radicatum) at Disko in West
Greenland. Note the onset of the decline in 1996, at the same time the winter ice coverage shortens (Fig.3).
Development of Salix arctica
Ground cover, %
50
LOC. 7
40
LOC. 4
30
20
10
0
1989 1990
1993 1996
1999 2001
2003
2006
Fig.2. Development in ground coverage of arctic willow (Salix arctica) in the same areas as for the monitoring of poppy plants. It
is most obvious that the rapid increase in ground cover decline has counteracted the loss of biomass in the poppy population.
Fig.3. Winter ice coverage in Disko Bay for most of the observation period showed in Figs 1 and 2 (Hansen et al. 2006). The
duration of ice coverage has decreased with almost two months from 1996, coinciding with the marked change in plant
performance.
References:
Arft, A. M., M. D. Walker, J. Gurevitch, J. M. Alatalo, M. S. Bret-Harte, M. Dale, M. Diemer, F. Gugerli, G. H. R. Henry, M. H.
Jones, R. D. Hollister, I. S. Jónsdóttir, K. Laine, E. Lévesque, G. M. Marion, U. Molau, P. Mølgaard, U. Nordenhäll, V.
Raszhivin, C. H. Robinson, G. Starr, A. Stenström, M. Stenström, Ø. Totland, P. L. Turner, L. J. Walker, P. J. Webber, J. M.
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Climate Change: Global Risks, Challenges and Decisions
IOP Conf. Series: Earth and Environmental Science 6 (2009) 312022
IOP Publishing
doi:10.1088/1755-1307/6/1/312022
Welker, and P. A. Wookey. 1999. Responses of Tundra Plants to experimental Warming: Meta-Analysis of the International
Tundra Experiment. Ecol. Monographs 69: 491-511. Hansen, B. U., B. Elberling, O. Humlum, and N. Nielsen. 2006.
Meteorological trends (1991-2004) at Arctic Station, Central West Greenland (69º15’N) in a 130 years perspective. Geografisk
Tidsskrift, Danish Journal of Geography 106: 45-55. Henry, G., and U. Molau. 1997. Tundra plants and climate change: the
International Tundra Experiment (ITEX). Global Change Biology 3: 1-9. Molau, U., and P. Mølgaard. 1996. ITEX Manual.
Danish Polar Center, Copenhagen. Mølgaard, P., and K. Christensen. 1997. Response to experimental warming in a population of
Papaver radicatum in Greenland. Global Change Biology 3 (Supplementum1): 116-124. Mølgaard, P., M. C. Forchhammer, L.
Grøndahl, and H. Meltofte. 2002. Blomsterne må vente på at sneen smelter og på varmen. Zackenberg: Temarapport 41, DMU:
43-46. Nielsen, N., O. Humlum, and B. U. Hansen. 2000. Meteorological Observations in 2000 at the Arctic Station,
Qeqertarsuaq (69°15’N), Central West Greenland. Geogr. Tidsskrift, Danish Journal of Geography 101: 155-158. Walker, M., C.
Wahren, R. Hollister, and G. Henry. et al. 2006. Plant community responses to experimental warming across the tundra biome.
Proceedings of the National Academy of Sciences 103: 1342-1346.
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